<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<script>
    var result=prompt('请输入您的分数');
    if(result >= 90 && result <= 100){
        alert('您的成绩为A');
    }else if(result >= 80 && result < 90){
        alert('您的成绩为B');
    }else if(result >= 70 && result < 80){
        alert('您的成绩为C');
    }else if(result >= 60 && result < 70){
        alert('您的成绩为D');
    }else{
        alert('您的成绩为E，或者您输入有错');
    }
</script>
<body>

</body>
</html>